The Orange Box is simply the best deal you'll find this generation.
Overall though, I think the main prize of the package is Portal. It's a short game, won't take you any more than 3-5 hours, but it's quite simply one of the most fun experiences I've had in a video game in quite some time. The dialogue is sharply and cleverly written, and the first person shooter - esque puzzle gameplay is top notch. Portal is something nobody should miss.
But let's not ramble. The Orange Box contians many of gaming's finest treasures, and even though Portal probably beats the hell out of any of them, they're all classics and must be played if you like first person shooters. Period.
Let's get technical. The graphics for The Orange Box actually vary quite vastly. The Half Life graphics haven't really been revamped that much, but then again, it looked amazing when it came out, so there isn't much too complain about in that department. You will find different visual styles in Team Fortress 2, mainly. TF2 contains some of the most wacky animated visuals I've ever seen, and it looks just about as good as a pixar flick. The visuals are quite charming and the game is almost as fun to watch as it is to play. On the other hand, there isn't much to Portal's visuals, but that's just because there doesn't need to be. You'll see when you play. Overall, the graphics you'll look at in The Orange Box are all fairly impressive, some better than others. They're all good in their own ways.
The sound effects are what you'd expect. In TF2, you'll hear very cartoonish booms and bangs when explosions occur, and the voices for the characters sound like they came straight from a bugs bunny show, in a very good way. Half Life 2's fantastic sound effects and voice acting are definitely existent, so no worries there. Portal's sound effects are pleasantly odd and humorous. But I won't give too much away.
In closing, The Orange Box is a game that every FPS fan must purchase. It's got 5 full games inside, and it's all for 60 dollars. And Valve obviously wasn't just thinking of quantity, but quality even more. Play this game for your own first person shooting - good.